WO2003052364A1

WO2003052364A1 - Method for producing a microstructure

Info

Publication number: WO2003052364A1
Application number: PCT/EP2002/014192
Authority: WO
Inventors: Martin Eickhoff; Stefan Kolb; Reinhard Wittmann
Original assignee: Infineon Technologies Ag
Priority date: 2001-12-17
Filing date: 2002-12-12
Publication date: 2003-06-26
Also published as: DE10161953A1

Abstract

The invention relates to a method for producing a microstructure comprising a substrate (1) and a structure that can be displaced in relation to said substrate (1). A spacer (7) is placed on a raw structure comprising the substrate (1), a sacrificial layer (2) on the substrate (1) and a patterned layer (3), whereby the sacrificial layer (2) is located between the patterned layer (3) and the substrate (1) and the spacer is inserted between the patterned layer (3) and the substrate (1). The material of the spacer (7) is different from that of the sacrificial layer (2) and can be dry-etched. Once the spacer (7) is in place, the sacrificial layer (2) is removed, in such a way that part of the spacer (7) remains. The spacer (7) is then removed by dry-etching.

Description

description

Method of making a microstructure

The present invention relates to the field of manufacturing microstructures, and more particularly to the field of manufacturing microstructures with movable elements.

Micromechanical components with one or more elements movable with respect to a substrate are used in many devices. For example, acceleration sensors or rotation rate sensors comprise movable structures, a movable structure serving as a sensor element for detecting mechanical physical quantities, such as an acceleration or an angular velocity. Consequently, the quality and the performance of a method for producing such a movable structure are of decisive importance for the behavior and the accuracy of the measurement of physical quantities in such components.

Conventionally, a sacrificial layer which is arranged between a substrate and the layer which is to serve as a movable structure is used to produce a movable structure. The sacrificial layer is partially or completely removed by wet chemical etching in order to form the movable structure, the etching agent used having to have a sufficient lateral etching rate in order to enable the etching of the sacrificial layer. When using the wet chemical etching to remove the sacrificial layer, however, the problem arises that when the etching solution dries, capillary forces occur, which often lead to mechanical contact between the movable one

Structure and the substrate lead. More specifically, this can result in the movable structure and the substrate forming an inseparable mechanical connection, since at the time point of etching the surfaces of the same are highly pure and chemically active. As the mobility of the movable structure is consequently no longer given by the fact that it adheres to the substrate, this leads to a total failure of the component, which increases the production costs per unit in mass production.

One way to avoid capillary forces and the associated adhesive bond during etching is to use gas phase etching. HF gas etching is conventionally used for this purpose, but it has the disadvantage that special devices are required for this, which go beyond the devices used in industrial semiconductor production. Furthermore, performing HF gas etching is complex and difficult to control.

Unfortunately, dry etching methods, which are used as standard in semiconductor production, cannot be used for etching the sacrificial layer because of the low lateral etching rates.

A known possibility of fixing the movable structure during the wet chemical etching is to use a so-called "lacquer plug" as described in DE19600399. In this case, lacquer is introduced into an opening in the sacrificial layer via an opening in the structure, the lacquer plug thus formed having a small spatial extent. After the sacrificial layer has been removed by means of a wet chemical etching, the lacquer plug can then be removed either by a dry chemical method, such as, for example, ashing in an oxygen plasma, or by an organic solvent with supercritical drying. However, this method has the disadvantage that reliable coating filling and residue-free coating removal are associated with technological difficulties for thick, movable structures. The object of the present invention is to provide an improved method for producing a microstructure with a movable element.

This object is achieved by a method according to claim 1 or 11.

The present invention is based on the finding that in the production of a moveable structural layer, an unwanted connection of a substrate and a moveable structural layer can be avoided by using a spacer between the substrate and the moveable structural layer, the material of which is chosen in this way is that the spacer essentially remains during the removal of a sacrificial layer which is arranged between the substrate and the movable structural layer and can be removed in a subsequent dry chemical etching after the removal of the sacrificial layer.

An advantage of the present invention is that the manufacture of a movable structural layer can be carried out without special equipment, which goes beyond standard equipment in semiconductor production, and in particular that the spacer can be removed by a dry etching process, in which an adhesive connection of the movable Structure and the substrate does not occur.

In one exemplary embodiment, the movable layer is applied to a first sacrificial layer, which is arranged on a substrate, wherein a second sacrificial layer is further provided on the movable layer, on which a cover layer is provided. Due to the use of a spacer material with great adhesion, the spacer can advantageously be used in this exemplary embodiment. be applied such that it is only connected to the cover layer. The adhesion achieved is sufficient to prevent irreversible adhesion of the movable structure during the removal of the first and second sacrificial layers. The resulting avoidance of a support that is compatible with both the substrate and the

Connected lid, is an advantage in that the fact that the shallow depth of the same is considerably facilitated.

Preferred exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. Show it:

La-f are schematic cross-sectional representations of an arrangement which undergoes a manufacturing process according to a first exemplary embodiment of the present invention; and

2a-e are schematic cross-sectional representations of an arrangement which undergoes a manufacturing process according to a second exemplary embodiment of the present invention.

Fig. La shows a cross-sectional view of an arrangement before going through a manufacturing process according to the present invention. The arrangement, which represents a raw structure for a component, such as a sensor element for detecting an acceleration or an angular velocity, has a substrate 1 made of a semiconductor material, on which a sacrificial layer 2 is applied on one side thereof. A structural layer 3, which is formed, for example, from a polycrystalline silicon material, is applied to the sacrificial layer 2, which preferably consists of an oxide which can be etched by wet chemistry, such as silicon oxide. The structure layer should form the movable structure after going through the manufacturing process. The structural layer has recesses that allow lateral etching of the sacrificial layer 2 to remove enable the same. The sacrificial layer 2 and the structural layer 3 are applied by means of known semiconductor techniques, such as, for example, a CVD process (CVD = chemical vapor deposition). The structuring of the structure layer 3 is likewise carried out by means of methods and devices which are known from standard semiconductor production and, for example, comprise conventional photolithography. The structural layer 3 comprises recesses in which the material of the structural layer 3 has been removed, so that the sacrificial layer 2 is exposed in these areas. The recesses in the structure layer 3 are formed by means of known methods, such as, for example, photolithography with a subsequent etching process.

Fig. Lb shows the arrangement of Fig. La after a first process step. In this process step, a coherent lacquer layer 4 made of a photoresist is first applied to the structure layer 3. Thereupon the lacquer layer 4 is removed over a recess of the structure layer 3 by means of known photolithography techniques, so that a channel 5 is formed through the recess in the structure layer 3 and the exposed area of the lacquer layer 4, which in the direction of the substrate 1 through the Sacrificial layer 2 is limited.

Fig. Lc shows the arrangement of Fig. La after the execution of a further process step. In this process step, a recess 6 is formed in the sacrificial layer 2 by an etching process. The etching process can be carried out by etching with an anisotropically etching agent or by etching with an anisotropically etching agent together with an isotropically etching agent, the etching agent in each case being fed via channel 5 to the opera layer 3 and attacking it. The use of a suitable anisotropic etching agent with a sufficient lateral etching rate has the effect that after the etching process, the recess 6 formed beyond the channel 5 formed The recess 6 has a boundary which extends laterally through a surface of the sacrificial layer 2, in the direction toward the substrate 1 through a surface of the substrate 1 and in the direction away from the substrate 1 through a section of the structural layer 3 is delivered. The lacquer layer 4 is then removed, so that the arrangement shown in FIG. 1c is obtained.

In a next process step, a spacer 7 is introduced in a deposition process. In the case of the deposition process, which is preferably a CVD process, the spacer material penetrates into the recess 6 and forms a coherent layer along the boundaries of the recess 6 and along lateral surfaces which form the passage to the recess 6 , whereby the spacer layer can be structured in such a way that a spacer layer can be structured so that it only remains in support areas by means of a subsequently applied mask, which consists, for example, of a photoresist layer structured by means of photolithography. The continuous layer that forms the spacer 7 is preferably formed such that it extends partially over a region of the surface of the structural layer 3, as shown in FIG. 1d, thereby anchoring the spacer 7 on the structural layer 3 is increased. In contrast to the process of a lacquer stopper, the spacer 7 is introduced in a defined and controllable manner, as a result of which the thickness and geometry can be designed as desired. Furthermore, the recess in the structural layer 3, through which the spacer material penetrates into the recess 6, can be kept small, as a result of which the space requirement is determined primarily by the available lithography and a use of the method according to the invention for MEMS structures (MEMS = micro electrical mechanical systems) in many sizes and designs. A nitride material is preferably used as the spacer material, the same being formed by means of known application techniques and preferably by means of a deposition in an LPCVD process (LPCVD = low pressure chemical vapor deposition). The use of a nitride layer is advantageous due to the high mechanical stability, as a result of which the thickness and geometry of the spacer 7 can be kept small. As a result, the method according to the invention is also suitable for arrangements in which movable structures of small order of magnitude are to be produced. In addition, the method of using a nitride layer, which is applied by means of an LPCVD method, enables the spacer 7 to be formed even for deep structures with a thick sacrificial layer, since the applied nitride layer has a very good edge coverage, as a result of which good layer adhesion is achieved , A further advantage of using a nitride layer results from the fact that nitride material has a substantially lower etching rate than the material of the sacrificial layer 2 in the case of wet chemical etching. Consequently, the thickness of the layer of the spacer 7 can be dimensioned such that, in the step of wet chemical etching of the sacrificial layer 2 described below, the spacer 7 is only slightly removed due to the lower etching rate of the nitride material compared to the sacrificial material and remains, so that Nitride layer can maintain a function as an elastic, distance-maintaining connection between the substrate 1 and the structural layer 3 during a subsequent etching process of the sacrificial layer 2.

FIG. 1e shows the arrangement after an etching process of the sacrificial layer 2. First, a protective layer, for example made of photoresist, is formed using known techniques in order to protect regions of the structural layer 3 against undesired etching. During the wet chemical etching process of the sacrificial layer 2, which preferably comprises an etching with HF, the etching agent engages through the recesses in the structural layer 3 to the sacrificial layer 2, the sacrificial layer 2 between the structural layer 3 and the substrate 1 being partially or completely removed due to a high lateral etching rate of the etchant.

The provision of the spacer 7 during the entire etching process and the subsequent drying process of the liquid etchant guarantees that the structural layer 3 is always kept at a distance from the substrate 1, so that the structural layer 3 does not bend and does not adhere to the substrate 1 is. Furthermore, the present invention offers the advantage that etching with a good lateral etching rate can be achieved with a suitable choice of the spacer.

After the arrangement has dried, the spacer 7 is removed by means of a dry chemical etching process, the arrangement shown in FIG. The etching process can be carried out in systems that are used as standard in semiconductor production. The use of a dry chemical etching process to remove the spacer 7 has the advantages of good controllability and removal of the spacer 7 without leaving residues. It has proven to be an advantage here that the spacer 7 can be formed with a small geometry and thickness, whereby a simple and residue-free removal of the same is additionally facilitated by means of a dry chemical etching process.

The arrangement shown in FIG. If with a structural layer 3 movable with respect to the substrate 1 can be used, for example, as a detection element in an acceleration sensor or a rotation rate sensor, the movable structure layer 3 serving as a sensitive element for detecting physical quantities.

The following is a second embodiment of the present invention with reference to Figures 2a-2e explained. In contrast to the first exemplary embodiment, in the second exemplary embodiment described below, the spacer 7 is introduced in such a way that it is connected to a cover 10 and a structural layer 3.

2a shows a raw structure of the second exemplary embodiment. A first sacrificial layer 8 is formed on a substrate 1, on which in turn a structural layer 3 is formed, which is to form the movable structure. As in the first exemplary embodiment, the structural layer 3 has recesses in order to enable lateral etching.

A second sacrificial layer 9 is formed on the structure layer 3 and in the recesses thereof. Furthermore, a cover 10 is formed on the second sacrificial layer 9, which has recesses to enable lateral etching, which are preferably formed above the recesses in the structural layer 3, as shown in FIG. 2a.

Like the sacrificial layer 2, the first sacrificial layer 8 and the second sacrificial layer 9 have a material that can be etched by wet chemistry, such as silicon oxide. The first 8 and second 9 sacrificial layers are used in this exemplary embodiment in order to keep the movable structure which is formed from the structure layer 3 movable with respect to the substrate 1 and the cover 10.

FIG. 2b shows the structure of FIG. 2a after a first etching process has been carried out to form a recess 6, in which the spacer 7 is introduced in a subsequent step.

In accordance with the formation of the recess 6 in the first exemplary embodiment, the recess 6 is formed by etching with an anisotropically etching agent or with an anisotropically etching agent together with an isoptrop-etching agent. The etchant is ne recess 11 in the cover 10 to the second sacrificial layer 9 is supplied. The use of the anisotropic etching agent causes the recess 6 in the second sacrificial layer 9 to extend laterally beyond the recess 11 of the cover 10.

In order to limit the etching process to the desired area, a photoresist is applied to the cover 10 and into the recesses thereof prior to the etching process, the area in which the recess 6 is to be formed being defined by suitable structuring by means of, for example, photolithography. The depth of the etching is regulated via the etching time.

After the recess 6 is formed, the spacer 7 is introduced by means of a deposition process and preferably by a CVD process, with reference to FIG. 2c. Since the recess 6 is only formed in the second sacrificial layer 9, the spacer 7 is formed as a coherent layer which extends along the boundary surfaces of the recess 6 and on an area of the cover 10.

The spacer 7 is applied in such a way that a coherent layer is first applied along the boundary surfaces of the recess 6, on the cover 10 and in recesses thereof. As has already been described in the first exemplary embodiment, the spacer 7 is then limited to the desired area by means of a photolithography and an etching step.

In a next process step, the first 8 and second 9 sacrificial layers are removed by wet-chemical anisotropic etching in accordance with the first exemplary embodiment. The first 8 and second 9 sacrificial layers are preferably removed in one process step. The spacer 7 prevents the structural layer 3 from coming into contact with the substrate 1 or the cover 10 during the etching step. In this exemplary embodiment, since the spacer is anchored to the cover 10 and not to the substrate 1 after the etching of the first 8 and second 9 sacrificial layer, in order to provide support for the structural layer 3, it is necessary to include the material for the spacer 7 to select a large adhesiveness in order to withstand the weight of the structural layer 3 and the cohesive forces generated during the etching.

As already mentioned in the first exemplary embodiment, nitrite, which has a high anchoring ability, is advantageously used for this purpose.

In a subsequent process step, the spacer

7 removed by dry chemical etching. This has an advantageous effect that the spacer 7 does not extend beyond the structural layer 2 due to the introduction from above and the anchoring to the cover 10 in depth.

The removal of the spacer 7 is thereby facilitated, which makes it possible to keep the diameter of the recess 11 of the cover 10 required to form the recess 6 or to form the spacer 7 small.

Furthermore, the method according to the second exemplary embodiment enables the first sacrificial layer by limiting the spacer 7 to the depth of the structural layer 3

8 and consequently a distance of the structural layer 3 from the substrate 1 can have a great length without the removal of the spacer 7 being difficult.

This cannot be achieved in particular with the known methods of using lacquer plugs, since the lacquer has only a low anchoring ability, so that the lacquer plug has to be applied to the substrate 1 during the etching of the sacrificial layers in order to avoid adhesion of the structure layers 3 in order to obtain a sufficient support effect for the structure layer 3. Consequently, in the known method of using lacquer plugs, removal of the lacquer plug is problematic since the lacquer must be removed from a great depth, which makes it necessary to provide the recess 11 with a correspondingly large diameter.

As previously mentioned, this is avoided by the spacer according to the invention.

After removal of the spacer 7, the movable structure 3 is freely movable with respect to the substrate 1 and the cover 10, the latter being connected at one edge to the substrate 1 and the cover 10 via remnants of the sacrificial layers 8 and 9.

Although the present invention has been described such that only one spacer is provided between the substrate and the structural layer, alternative embodiments of the present invention include providing multiple spacers between the substrate and the structural layer.

LIST OF REFERENCE NUMBERS

1 substrate

2 sacrificial layer 3 structural layer

4 lacquer layer

5 channel

6 recess

7 spacers 8 first sacrificial layer

9 second sacrificial layer

10 cover

11 recess

Claims

claims

1. A method for producing a microstructure with a substrate (1) and a structure that is movable with respect to the substrate (1), comprising the following steps:

Providing a raw structure which comprises the substrate (1), a sacrificial layer (2) on the substrate (1) and a structural layer (3), the sacrificial layer (2) being arranged between the structural layer (3) and the substrate (1) ;

Introducing a spacer (7) between the structural layer (3) and the substrate (1), the spacer (7) being made of a different material than the sacrificial layer (2) and the material of the spacer (7) being dry-etchable ;

Removing the sacrificial layer (2) such that the spacer (7) remains at least partially; and

Remove the spacer (7) using dry etching.

2. The method according to claim 1, wherein the spacer (7) is made of a nitride material.

3. The method according to any one of claims 1 or 2, wherein the step of introducing a spacer (7) comprises producing a recess (6) in the sacrificial layer (2).

4. The method according to any one of claims 1 to 3, wherein the step of introducing a spacer (7) an application of a continuous layer as a spacer ter (7), the same extending at least over a section of the substrate (1) and a section of the structural layer (3).

5. The method according to claim 4, wherein the removal of the sacrificial layer (2) comprises a wet chemical etching process.

6. The method according to any one of claims 3 to 5, wherein the step of producing a spacer (7) comprises producing a recess (6) in the sacrificial layer (2) by anisotropic etching.

7. The method according to any one of claims 3 to 5, wherein the step of creating a spacer (7) comprises creating a recess (6) in the sacrificial layer (2) by a combination of an isotropic and an anisotropic etching.

8. The method according to any one of claims 5 to 7, wherein the thickness and geometry of the spacer (7) is selected such that the same remains essentially when the sacrificial layer (2) is removed by means of a wet chemical etching process.

9. The method according to any one of claims 4 to 8, wherein the step of introducing a spacer (7) comprises applying a continuous layer as a spacer (7) by means of an LPCVD method.

10. The method according to any one of claims 4 to 9, wherein the step of providing a raw structure comprises providing a raw structure for a microstructure, in which the structure layer defines a movable mass of an acceleration sensor or a rotation rate sensor.

11. Method for producing a microstructure with a substrate, a cover and one with respect to the substrate and the cover movable structure with the following steps:

Provision of a raw structure with the following features:

a first sacrificial layer applied to the substrate;

a structure layer that is applied to the first sacrificial layer;

a second sacrificial layer which is applied to the structure layer; and

a cover applied to the second sacrificial layer;

Introducing a spacer between the structural layer and the cover, the spacer being made of a different material than the sacrificial layer, and the material of the spacer being dry-erasable;

Removing the first and second sacrificial layers such that the spacer remains at least partially; and

Remove the spacer using dry etching